Advanced body armor utilizing shear thickening fluids

ABSTRACT

An armor composite material has been invented which contains a fabric which has been impregnated with shear thickening fluid. This invention offers a ballistic resistant material that is more flexible and less bulky than comparable, conventional ballistic fabric. The material in the alternative can be puncture resistant. The invented material offers superior ballistic performance and/or puncture resistance compared to conventional ballistic fabric-based materials of equal thickness. The invented material can be applied to applications requiring armor that is compact and/or flexible, such as body armor, protective clothing and flexible protective devices and shields, and stab resistant clothing and devices.

GOVERNMENT LICENSE RIGHTS

The United States Government has rights in this invention as providedfor by Army Research Laboratories, CMR contract nos. DAAD19-01-2-0001and DAAD19-01-2-0005.

BACKGROUND OF THE INVENTION

Body armor is essential equipment for police and military. Currently,body armor is fielded only in specific high-risk scenarios, and istypically limited to chest and head protection. However, a significantpercentage of battlefield injuries occur to the extremities, includingarms, legs, hands, and neck. Armor for these extremities must offerprotection from fragment and ballistic threats, without significantlylimiting soldier mobility and dexterity.

Conventional body armor materials are typically comprised of many layersof polyaramid poly(phenylene diamine terephthalamide) fabric, sold byDuPont under the registered name of Kevlar®, with optional ceramic tileinserts. These materials are too bulky and stiff for application inextremities protection. A material is needed which can offer theequivalent ballistic performance of existing body armor materials, butwith significantly more compactness and flexibility.

Shear thickening is a non-Newtonian flow behavior often observed inconcentrated colloidal dispersions, and characterized by a large,sometimes discontinuous increase in viscosity with increasing shearstress (Lee and Reder, A. S. TAPPI Coating Conference Proceedings, p.201, 1972; Hoffman, R. L., J. Colloid Interface Sci., Vol. 46, p. 491,1974; Barnes, H. A., J. Rheol., Vol. 33, p. 329, 1989). It has beendemonstrated that reversible shear thickening in concentrated colloidalsuspensions is due to the formation of jamming clusters resulting fromhydrodynamic lubrication forces between particles, often denoted by theterm “hydroclusters” (Bossis and Brady, J. Chem. Phys., Vol. 91, p. 866,1989; Foss and Brady, J. Fluid Mech., Vol. 407, p. 167, 2000; Catherallet al., J. Rheol., Vol. 44, p. 1, 2000). The mechanism of shearthickening has been studied extensively by rheo-optical experiments(D'Haene et al., J. Colloid Interface Sci., Vol. 156, p. 350, 1993;Bender and Wagner, J. Colloid Interface Sci., Vol. 172, p. 171, 1995),neutron scattering (Laun et al., J. Rheol., Vol. 36, p. 743, 1992;Bender and Wagner, J. Rheol., Vol. 40, p. 899, 1996; Newstein, et al.,J. Chem. Phys., Vol. 111, p. 4827, 1999; Maranzano and Wagner, J.Rheol., Vol. 45, p. 1205, 2001a; Maranzano and Wagner, J. Chem. Phys.,2002) and stress-jump rheological measurements (Kaffashi et al., J.Colloid Interface Sci., Vol. 181, p. 22, 1997). The onset of shearthickening in steady shear can now be quantitatively predicted(Maranzano and Wagner, J. Rheol., Vol. 45, p. 1205, 2001a, and Maranzanoand Wagner, J. Chem. Phys., Vol. 114, p. 10514, 2001) for colloidalsuspensions of hard-spheres and electrostatically stabilizeddispersions. This shear thickening phenomenon can damage processingequipment and induce dramatic changes in suspension microstructure, suchas particle aggregation, which results in poor fluid and coatingqualities. The highly nonlinear behavior can provide a self-limitingmaximum rate of flow that can be exploited in the design of damping andcontrol devices (Laun et al., J. Rheol., Vol. 35, p. 999, 1991; Helberet al., J. Sound and Vibration, Vol. 138, p. 47, 1990).

The general features of containment fibers for use in energy dissipatingfabrics are high tenacity and high tensile modulus. These materials arealso considered ballistic materials. At the same time, in manyapplications, it may be desirable to utilize a fabric having thebenefits of relative low bulk and flexibility. To achieve suchproperties, polymeric fibers may be used. The fibers which may bepreferred include aramid fibers, ultra-high molecular weightpolyethylene fiber, ultra-high molecular weight polypropylene fiber,ultra-high molecular weight polyvinyl alcohol fiber and mixturesthereof. Typically, polymer fibers having high tensile strength and ahigh modulus are highly oriented, thereby resulting in very smooth fibersurfaces exhibiting a low coefficient of friction. Such fibers, whenformed into a fabric network, exhibit poor energy transfer toneighboring fibers during an impact event. This lack of energy transfermay correlate to a reduced efficiency in dissipating the kinetic energyof a moving object thereby necessitating the use of more material toachieve full dissipation. The increase in material is typically achievedthrough the addition of more layers of material which has the negativeconsequence of adding to the bulk and weight of the overall fabricstructure.

Among the most common uses for these so-called containment fabrics arein the use of body armor, and windings surrounding the periphery ofturbine engines such as those found on commercial aircraft. Such anapplication is disclosed in U.S. Pat. No. 4,425,080 to Stanton et al.the teachings of which are incorporated herein by reference. The fabricis intended to aid in the containment of a projectile which may bethrown outwardly by rotating parts within the engine in the event of acatastrophic failure.

While the overall energy dissipating capacity of the fabric windingssurrounding the engine is important, minimizing the thickness of thewindings is also critical. Furthermore, economic considerations dictatethat the number of fabric layers utilized for this purpose cannot beexcessive. Thus, an effective containment structure should not requirean excessive number of fabric layers to achieve the necessary levels ofenergy containment. It has been determined that the seeminglyconflicting goals of improved kinetic energy containment and reducedmaterial layers can, in fact, be achieved by improving the energytransfer between the adjacent fibers or yarns at the location of impactin the fabric network.

Several techniques are known for increasing the energy transferproperties between fibers or yarns but each of these known techniqueshas certain inherent deficiencies. One known method is to roughen thesurface of the fibers or yarns by sanding or corona treatment. However,such roughening is believed to have limited utility due to the resultantdegradation in the fiber.

Another method of increasing energy transfer between adjacent fibers oryarns is to coat the fabric with a polymer having a high coefficient offriction. One deficiency in this practice is the formation offiber-to-fiber bonds. Such bonding may result in stress reflections atyarn crossovers during impact by a moving article, which cannot betransferred away from the impact region. Another deficiency is the largeweight gain typical of coatings, which may be ten percent or more. Afurther limitation of this approach is a significant decrease in fabricflexibility due to the addition of the relatively stiff polymer coating.A related method is to use a sticky resin that creates adhesion betweenthe fibers, as disclosed in U.S. Pat. No. 1,213,118 to Lynch, but thistechnique has the same inherent deficiencies of fiber to fiber bondingand increased weight as exhibited by coatings.

Yet another method for improving the energy transfer between fibers oryarns in a containment fabric is core spinning of high strength fibersin combination with weaker fibers having a higher coefficient offriction as disclosed in U.S. Pat. No. 5,035,111 to Hogenboom. However,these relatively high friction fibers may reduce the overall fabricstrength.

Dischler et al. (U.S. Pat. No. 5,776,839) used Kevlar® fibers coatedwith a dry powder that exhibits dilatant properties. Dilatant propertiesrefer to increases in both volume and viscosity under flow. In theirwork, the fibers demonstrated an improved ability to distribute energyduring ballistic impact due to the enhanced inter-fiber friction.

Schuster et al (U.S. Pat. No. 5,854,143) also describe the use of drydilatant agents in a fabric carrier to improve ballistic protection. Intheir approach, the dilatant agent is a polymeric powder which isapplied to the fabric while suspended in a carrier fluid, andsubsequently dried to leave behind the dilatant solid.

Gates (U.S. Pat. No. 3,649,426) describes the use of a dilatantdispersion consisting of small rigid particulates suspended in anenvironmentally stable liquid, such as glycerin. In this case, thesolid-liquid dispersion is dilatant, and remains flowable in the armormaterial. The dilatant dispersion is confined in flexible cellularcompartments which could be placed behind conventional protectivearmors. However, the necessity of a cellular containment structureresults in a material system which is bulky, heavy, and relativelyinflexible.

SUMMARY OF THE INVENTION

In light of the above background, it will be appreciated that a needexists for a fabric and articles formed therefrom having an improvedability to dissipate the kinetic energy of a moving object in comparisonto known structures. The moving object can be a projectile, such asflying metal or piercing object, such as, but not limited to a knife orsword. The material alternatively can have properties of stabresistance. It is also possible that the object is not a moving but thearticle or person wearing the material is moving. For example, a tire ofan automobile or bicycle, etc can be made of a material according to theinvention and can roll over a nail, glass etc. and would not puncturebecause of the puncture resistance of the material.

It is a feature of the present invention to provide a fabric andarticles formed therefrom comprising high strength, high moduluspolymeric fibers or yarns impregnated with a fluid that exhibits shearthickening properties, herein referred to as a “shear thickening fluid”(or “STF”). The STF remains flowable after impregnation, so as to notimpede fabric flexibility, but modifies the coefficient of frictionbetween the fibers or yarns by rigidizing during an impact event.

In another embodiment according to the invention, the invention can bean article that comprises a plurality of layers. At least one of thelayers is impregnated with the STF, while other layers may beunimpregnated.

According to one aspect of the present invention, a fabric fordissipating the kinetic energy of a moving object is provided. Thefabric is formed by an arrangement of high tenacity polymer fibers. Thefibers are impregnated with particles suspended in a solvent.

According to a more particular aspect of the present invention, aprotective encasement of fiber material is provided. The fiber materialcomprises a plurality of high tenacity polymer fibers formed into aknitted, woven, or nonwoven fabric structure impregnated with particlessuspended in a solvent. The protective encasement may include layers ofsuch fabric surrounding a dynamic environment such as a turbine engine.

Stab and puncture resistant are used interchangeability throughout theapplication.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a ballistic test frame and target geometry accordingto the invention.

FIG. 2 illustrates flexibility test geometry that was used according tothe invention.

FIG. 3 illustrates Scanning Electron Microscopy (“SEM”) of KEVLAR® weaveimpregnated with the STF fluid.

DETAILED DESCRIPTION OF THE INVENTION

The invention is directed to a material such as fabric materials andarticles formed therefrom comprising high strength, high moduluspolymeric fibers or yarns impregnated with a fluid, composed ofparticles suspended in a solvent, which undergoes a shear-thickeningtransition such that the coefficient of friction between the fibers oryarns is increased during an impact event.

The fabrics comprising high tenacity fibers have been incorporated as animportant element in containment structures used to dissipate thekinetic energy of moving objects and thereby prevent passage of thosemoving objects through such containment structures to a person orstructure to be protected against direct contact and damage by suchmoving objects. Fibers which can be used include, but are not limitedto, aramid fibers such as poly (phenylenediamine terephthalamide),graphite fibers, nylon fibers, glass fibers and the like.

Nylon would have an advantage if a lighter weight and cheaper materialis desired.

If the article has a plurality of layers, then each layer containing amaterial, preferably a ballistic material can be comprised of the sameor different materials. In other words it is possible to have aplurality of layers, such as a twenty-eight layer article that containsdifferent layers of different materials that dissipate the kineticenergy or are stab resistant or puncture resistant. For example, some ofthe layers can use a Kevlar® impregnated with STF, while other layerscan use a different ballistic or puncture resistant material such asnylon fibers impregnated with STF and other layers can benon-impregnated Kevlar®. The outer layers closest to the body or theobject being protected, do not have to be impregnated with STF. Thelayers impregnated with STF are preferably integrated into the articleand are not just the exterior layer closest to the object or body beingprotected.

The STF is the combination of the particles suspended in the solvent.

The particles used can be made of various materials, such as, but notlimited to, SiO₂ or other oxides, calcium carbonate, or polymers, suchas polystyrene or polymethylmethacrylate, or other polymers fromemulsion polymerization. The particles can be stabilized in solution ordispersed by charge, Brownian motion, adsorbed surfactants, and adsorbedor grafted polymers, polyelectrolytes, polyampholytes, or oligomers.Particle shapes include spherical particles, elliptical particles, ordisk-like or clay particles. The particles may be synthetic and/ornaturally occurring minerals. Also, the particles can be eithermonodisperse, bidisperse, or polydisperse in size and shape.

Any particle that has a size less than the yarn size, which is about 1mm, can be used. Preferably the particles should have a size less thanthe diameter of the fiber, which is typically 100 microns or less, sothat the particles can be impregnated and embedded in the weave of thematerial.

The solvents that are used can be aqueous in nature (i.e. water with orwithout added salts, such as sodium chloride, and buffers to control pH)for electrostatically stabilized or polymer stabilized particles, ororganic (such as ethylene glycol, polyethylene glycol, ethanol), orsilicon based (such as silicon oils, phenyltrimethicone). The solventscan also be composed of compatible mixtures of solvents, and may containfree surfactants, polymers, and oligomers. The solvents should beenvironmentally stable so that they remain integral to the fabric andsuspended particles during service.

The particles are suspended in the solvent and should produce a fluidthat has the shear thickening property. Shear thickening does notrequire a dilatant response, i.e. it may not be associated with anincrease in volume such as often observed in dry powders or sometimes insuspensions of larger particles (greater than 100 microns). The fluidmay be diluted with a second solvent to enable impregnation of thefabric, and then reconcentrated through evaporation of the secondsolvent after impregnation, as long as the remaining impregnated fluidremains a flowable liquid with shear thickening properties.

The ballistic properties of woven fabrics, such as, but not limited to,Kevlar® fabrics, are improved through impregnation with fluids thatexhibit the shear thickening effect. At low strain rates, for exampleassociated with normal motion of the wearer of a body armor system, thefluid will offer little impediment to fabric flexure and deformation.However, at the high strain rates associated with a ballistic impactevent, the fluid will increase in viscosity and in doing so, enhance theballistic protection of the fabric. The STF used in the targets iscomposed of particles suspended in a solvent.

EXAMPLE 1 Ballistic Performance

In the following examples silica particles (Nissan Chemicals MP4540)were suspended in ethylene glycol, at a volume fraction of approximately0.57. The average particle diameter, as measured using dynamic lightscattering, was determined to be 446 nm. Rheological measurements haveshown that this STF undergoes a shear thickening transition at a shearrate of approximately 10²-10³s⁻¹. Additionally, this transition isreversible, i.e. this liquid-to-solid transition induced by flow is notassociated with particle aggregation, nor does it result in anyirreversible change in the dispersion. Full details regarding thepreparation and rheological properties of the STF can be found in Lee etal., J. Mat. Sci., 38 pps. 2825-2833 (2003) and Lee and Wagner Rheol.Acta., 2002.

The Kevlar® fabric used in all composite target constructions was 600denier plain-woven Hexcel-Schwebel high performance fabric Style 706composed of Kevlar® KM-2 aramid fibers (poly-paraphenyleneterephthalamide) with an areal density of 180 g/m².

Target Preparation

To facilitate impregnation of the STF into the KEVLAR® fabric, an equalvolume of ethanol (22.0 dyne/cm) was added to the original ethyleneglycol (surface tension=47.7 dyne/cm) based STF. This diluted STF wasobserved to spontaneously impregnate the fabric. Following impregnation,the composite fabric was heated at 80° C. for 20 minutes in a convectionoven to remove the ethanol from the sample. The final composition of theimpregnated STF is 57 vol% silica in ethylene glycol. Microscopy hasconfirmed that this process results in the full impregnation of the STFinto the KEVLAR® fabric, as STF wetting is observed at the filamentlevel (Lee et al., J. Mat Sci., 38 pps. 2825-2833 (2003)). Impregnationof the fibers with the shear thickening fluid is shown in FIG. 2 of Leeet al. which corresponds to FIG. 3 of this application. FIG. 3 of thisapplication illustrates Scanning Electron Microscopy (“SEM”) of KEVLAR®weave impregnated with the STF fluid. The figure shows silica particlesdispersed within the yarn, demonstrating that the original STF wasimpregnated between the individual KEVLAR® fibers within each yarn. TheSTF was intercalated (inserted between fibrils) in the yarn as well asintercalated (inserted between yarns) in the fabric. The termsintercalated and impregnated used in the specification are synonymous.

A schematic diagram of a ballistic target is given in FIG. 1. Two piecesof 5.08 cm×5.08 cm aluminum foil (50 mm thickness) were used toencapsulate the targets 10. The Kevlar® layers were cut to 4.76 cm×4.76cm, impregnated with varying amounts of STF per layer (2, 4, and 8 ml)as indicated, and then assembled into the targets 10. To prevent leakageof STF out of the target assembly, heat-sealed polyethylene film(Ziplock bags sealed using a ULINE KF-200HC heat sealer) was used toencapsulate the targets.

All targets 10 were backed with a backing 20. The backing 20 contained asingle ply of unimpregnated Kevlar®, glued to a 5.08 cm diameter copperhoop (0.635 cm wire diameter) using Liquid Nails adhesive (ICI), inorder to help support the target during testing. In all cases the gluedKevlar® layer, backing 20, was immediately adjacent to the ballistictarget 10, with the copper hoop resting inside of the target mountingframe 30. All subsequent descriptions of ballistic targets 10 will listonly the Kevlar® layers within the aluminum foil layers, and do notinclude this individual backing 20 Kevlar® layer.

Ballistic Tests

The ballistic tests were performed using a smooth bore helium gas gun.All tests were performed at room temperature. The gun was sighted on thetarget center and the impact velocity was adjusted to approximately 244m/s (800 feet per second “fps”). The exact impact velocity of eachprojectile 40 was measured with a chronograph immediately beforeimpacting the target 10. The projectile 40 is a NATO standard fragmentsimulation projectile (“FSP”), consisting of a chisel-pointed metalcylinder of 1.1 grams (17 grains) and 0.56 cm diameter (22 caliber). A10.16 cm×10.16 cm×2.54 cm thick aluminum block 30 was cut with arecessed square hole to accept the 5.08 cm square target package asshown in FIG. 1. The target was held in place using light pressure fromspring clips located along its edge. The mounting block was then clampedonto a steel frame in line with the gas gun barrel.

A clay witness 50 was used to measure the depth of indentation (NIJstandard-0101.04, 2001) (FIG. 1). Modeling clay (Van Aken International)was packed into a 15.24 cm×8.89 cm×8.89 cm wooden mold, compressed witha mallet, and cut into four 7.62 cm×4.45 cm square pieces. This processminimizes air bubbles or poor compaction in the clay witness. The moldedclay block was held onto the back of the target using a strip ofadhesive tape. When comparing the ballistic performance of differenttargets, higher performance is demonstrated by smaller measured valuesof depth of indentation, which indicate that more energy was absorbed bythe target.

The deformation rate on the fluid during the ballistic event isestimated to be on the order of 10⁴-10⁵S⁻¹ (deformationrate˜V_(i)/projectile diameter=244 m/s/0.056 m). This rate is expectedto be sufficient to rigidize the STF, since it exceeds the criticalshear rate for the STF.

Flexibility and Thickness Tests

Two-dimensional drape tests were performed to measure the flexibility ofthe targets, as shown in FIG. 2. In all cases a 20 g weight 60 was used,and encapsulated ballistic targets were used as the test specimens 70.Bending angle is reported as a measure of target flexibility, withlarger angles indicating greater flexibility. Target thickness at thecenter of the targets was also measured with a micrometer.

Results

Table 1 compares the performance of targets A, B, and C: 2 ml of STFimpregnated into 4 layers of neat Kevlar, 10 layers of neat Kevlar, and4 layers of neat Kevlar, respectively. Targets A and B have comparableweights. However, target A, which is an STF-Kevlar composite, exhibitsbetter ballistic performance than target B, the neat Kevlar target.Furthermore, the STF-Kevlar composite (A) has fewer layers of Kevlar,more flexibility, and less thickness than the neat Kevlar target (B).Also note that the flexibility and thickness of targets A and C arecomparable. This result demonstrates that STF addition can greatlyimprove the ballistic properties of Kevlar fabric, without significantlyincreasing its rigidity or thickness.

TABLE 1 Comparison of flexibility of various targets with comparableballistic resistance but varying composition. Pene- Sample Sample Impacttration Bending Thick- Sample Weight Velocity Depth Angle, ness TargetDescription (g) (m/s) (cm) (°) (mm) A 2 ml STF 4.8 243 1.23 51 1.5impregnated in 4 layers of Kevlar ® B 10 layers of 4.7 247 1.55 13 3.0Kevlar ® C  4 layers of 1.9 244 2.12 50 1.4 Kevlar ®

Table 2 compares the ballistic performance of target A, which containsimpregnated STF, with target D, a composite composed of ethylene glycol(a Newtonian, non-shear-thickening fluid) impregnated into Kevlarfabric. Target C, which is composed of 4 layers of Kevlar, is providedfor reference. All three targets have equal numbers of Kevlar fabriclayers. However, the STF-impregnated target (A) is observed to havesuperior ballistic resistance as compared to target D, which containsthe carrier fluid without the shear thickening phenomena. In fact,target D performs comparable to target C, which is much lighter and onlycontains the Kevlar without carrier fluid or STF. This result shows thatthe shear-thickening properties of the impregnated fluid are critical toenhancing ballistic performance, and that the increase in ballisticperformance is not just due to an increase in target weight.

TABLE 2 Comparison of ballistic performance of STF- impregnated Kevlarwith ethylene glycol-impregnated Kevlar. Sample Impact PenetrationSample Weight Velocity Depth Target Description (g) (m/s) (cm) A 2 mlSTF 4.8 243 1.23 impregnated in 4 layers of Kevlar ® C 4 layers of 1.9247 2.12 Kevlar ® D 4 ml ethylene 6.3 246 2.20 glycol impregnated in 4layers of Kevlar ®

Table 3 compares the ballistic performance of target E, which consistsof 8 ml STF impregnated into 4 layers of Kevlar, with target F, whichcontains 8 ml of STF encased in a polyethylene film, stacked on top of 4layers of Kevlar fabric. Both targets E and F possess the same type andquantity of STF and Kevlar. However, target E has the STF impregnatedinto the fabric, while target F stacks the two materials independently.The results show that the impregnated target performs better than thestacked target. This result demonstrates that impregnation of the STFinto the Kevlar fabric is critical to fully realize the enhancement ofballistic performance.

TABLE 3 Comparision of ballistic performance of STF-impregnated Kevlarwith STF stacked on top of neat Kevlar. Sample Impact Penetration SampleWeight Velocity Depth Target Description (g) (m/s) (cm) E 8 ml STFimpregnated 13.9 253 0.673 into 4 layers of Kevlar F 8 ml of STFencapsulated, 13.9 247 1.72 stacked on top of 4 layers of neat Kevlar

Table 4 shows that increasing the volume of STF added to a fixed numberof Kevlar fabric layers increases the ballistic resistance of thefabric. Target C is composed of 4 layers of pure Kevlar. Each followingtarget (targets A, G, E) is impregnated with an increasing increment of2 ml of STF. As shown in Table 4, each additional 2 ml of shearthickening fluid results in a substantial increase in ballisticresistance. This data series reinforces the result that the presence ofthe STF impregnated into the target has a significant beneficial effectin creating ballistic resistance.

TABLE 4 Ballistic performance of targets with 4 layers of Kevlar anddifferent volumes of impregnated STF. Sample Impact Penetration WeightVelocity Depth Sample Description (g) (m/s) (cm) C 4 layers of Kevlar1.9 244 2.12 A 2 ml STF 4.8 243 1.23 impregnated in 4 layers of Kevlar G4 ml STF 7.9 244 0.886 impregnated in 4 layers of Kevlar E 8 ml STF 13.9253 0.673 impregnated in 4 layers of Kevlar

Table 5 compares the ballistic performance of targets A, G, and E, whichcontain Kevlar fabric with increasing amounts of impregnated STF, totargets X1, X2, and X3, which contain Kevlar fabric with increasingamounts of impregnated dry silica. Target C, which is composed of 4layers of Kevlar, is provided for reference. All seven targets haveequal numbers of Kevlar fabric layers. The dry silica targets (X1, X2,X3) have superior ballistic resistance as compared to target C, whichcontains only neat Kevlar fabric. However, the STF-impregnated targets(A, G, E) have superior ballistic resistance as compared to the drysilica-impregnated targets (X1, X2, X3) of comparable weight. Thisresult shows that a flowable shear-thickening fluid impregnated into afabric provides superior ballistic resistance as compared to fabricsreinforced by dry powders only.

TABLE 5 Comparison of ballistic performance of STF-impregnated Kevlarwith dry silica-impregnated Kevlar. Sample Impact Penetration SampleWeight Velocity Depth Target Description (g) (m/s) (cm) C 4 layers ofKevlar 1.9 244 2.12 A 2 ml STF impregnated in 4 4.8 243 1.23 layers ofKevlar G 4 ml STF impregnated in 4 7.9 244 0.886 layers of Kevlar E 8 mlSTF impregnated in 4 13.9 253 0.673 layers of Kevlar X1 3 g dry silicaimpregnated 4.9 252 1.42 in 4 layers of Kevlar X2 6 g dry silicaimpregnated 7.9 234 1.22 in 4 layers of Kevlar X3 12 g dry silicaimpregnated 13.9 225 0.89 in 4 layers of Kevlar

Table 6 shows that varying the impregnation pattern of the target fromlayer-to-layer, and varying the pattern of impregnation within a singlelayer, can be used to enhance the ballistic performance of the fabric.Comparison of Target H to Target C demonstrates that including a fewlayers of Kevlar impregnated with STF can significantly enhanceballistic resistance over the equivalent number of neat Kevlar layers(Target C). Furthermore, Target I is composed of a small amount of STFimpregnated into the Kevlar in a “striped” pattern. Comparison of TargetI to Target J demonstrates that the impregnation of the STF into thetarget can be “patterned”, i.e. need not be fully impregnated and stillresult in substantial increases in ballistic resistance. Further,comparison of the performance of Target I and Target J, both composed of6 layers of Kevlar, shows that even a very small amount of STFimpregnated into the fabric results in enhanced ballistic performance.

TABLE 6 Ballistic performance of targets with varying impregnationpatterns within a fabric layer, and between fabric layers. Sample ImpactPenetration Sample Weight Velocity Depth Target Description (g) (m/s)(cm) C 4 layers of Kevlar 1.9 244 2.12 H 2 layers of neat 13.9 242 0.787Kevlar, stacked on top of 8 ml of STF impregnated into 2 layers ofKevlar I 0.22 ml of STF 3.18 254 1.4 impregnated into 6 layers of Kevlarfabric, with a striped impregnation pattern in each fabric layer J 6layers of Kevlar 2.82 254 1.7

Table 7 shows that similar enhancements in performance have beenachieved with different particles and solvents impregnated into theKevlar® fabrics:

Table 7, sample K, which is composed of 450 nm silica particles coatedwith an adsorbed polymer, poly(vinyl alcohol) and dispersed in ethyleneglycol, shows enhanced ballistic resistance comparable to theperformance of sample A.

Table 7, sample L shows results for a shear thickening fluid composed ofsilica particles (450 nm) dispersed in a polymeric solvent, polyethyleneglycol (PEG), where similar enhancement in ballistic performance isachieved as for the molecular ethylene glycol formulations.

Table 7, sample M shows a formulation using much smaller silicaparticles, 30 nm, in polyethylene glycol (PEG), which shows significantballistic resistance that is comparable to samples with the largerparticle sizes (450 nm).

Table 7, sample N shows nonspherical particles consisting ofelliptically shaped calcium carbonate ellipsoidal particles in ethyleneglycol. This formulation shows enhancement in ballistic resistancecomparable to the spherical particles.

As shown the STFs can vary in carrier fluid type, particle type, andsurface functionalization, but all STFs tested successfully enhanceballistic performance.

TABLE 7 Ballistic performance of impregnated Kevlar targets withdifferent types of STF. Sample Impact Penetration Sample Weight VelocityDepth Target Description (g) (m/s) (cm) A 2 ml STF (450 nm spherical 4.8243 1.23 silica in ethylene glycol) impregnated into 4 layers of KevlarK 2 ml STF (450 nm 4.9 259 0.74 polymer-stabilized spherical silica inethylene glycol) impregnated into 4 layers of Kevlar L 2 ml STF (450 nmspherical 4.9 246 1.8 silica in polyethylene glycol) impregnated into 4layers of Kevlar M 2 ml STF (30 nm spherical 5.3 331 1.57 silica inpolyethylene glycol) impregnated into 4 layers of Kevlar N 1.6 ml STF(anisotropic 4.8 244 0.48 CoCO3 particles in ethylene glycol)impregnated into 4 layers of Kevlar

EXAMPLE 2 Stab Performance

In the following examples silica particles (Nippon Shokubai SeahostarKE-P50) were suspended in polyethylene glycol, at a volume fraction ofapproximately 0.52. The average particle diameter, as measured usingdynamic light scattering, was determined to be 450 nm. The Kevlar fabricused was 600 denier plain-woven Hexcel-Schwebel high performance fabricStyle 706 composed of Kevlar® KM-2 aramid fibers (poly-paraphenyleneterephthalamide) with an areal density of 180 g/m².

Two targets are compared: 15 layers of neat Kevlar fabric, with an arealdensity of 2670 g/m², and 12 layers of STF-Kevlar, with an areal densityof 2650 g/m². The STF-Kevlar sample was prepared according to themethods in Example 1. Note that both targets have comparable arealdensities. The neat Kevlar sample is approximately 25.4 cm×35.6 cm,while the STF-Kevlar sample is approximately 50.8 cm×35.6 cm.

Stab resistance measurements were performed using an end effectorfabricated according to the “spike” specifications of the U.S. NationalInstitute of Justice (NIJ) standard 115.00 (2000). This end effectormodels an ice pick or other puncturing threat, which are representativeof the types of improvised weapons often encountered by correctionalofficers. The end effector was mounted to a variable drop mass at aheight of 10 cm in a drop tower, so that all impacts occur at a velocityof approximately 1.4 m/s.

The target is placed on top of a multi-layer foam backing, arrangedaccording to NIJ standard 115.00 (2000). This backing consists of fourlayers of 5.8-mm-thick neoprene sponge (SCE45B from Rubberlite Inc.),followed by one layer of 31-mm-thick polyethylene foam (LD45 fromRubberlite Incorporated), followed by two layers of 6-mm-thick rubber(Duromater Rubber from PCF Foam Corp.). One layer of witness paper isplaced immediately behind the target (on top of the foam backing), withfour additional witness paper layers placed behind each of the fourlayers of neoprene sponge. The witness paper used is 140 g/m² syntheticpaper from Polyart.

For each test, the weighted spike is dropped onto the target. Thewitness papers are then inspected to determine how many layers ofwitness paper were punctured by the spike. Fewer layers of puncturedwitness paper indicates superior puncture resistance for the armortarget. Note that the maximum number of witness paper layers that can bepenetrated is 5 (the total number of witness paper layers).

Table 8 compares the stab results for the neat and STF-Kevlar samples.For the neat Kevlar sample, witness papers are penetrated at all energylevels, with increasing penetration as impact energy increases. Notethat, at energy levels of 3.30 J and above, all 5 layers of witnesspaper are penetrated. In contrast, the STF-Kevlar sample preventspenetration of the witness papers at all energy levels. Note that, forthe STF-Kevlar targets, the first layer of witness paper is neverpenetrated, indicating that the spike does not penetrate through thearmor target. Also note that the areal densities of the neat Kevlar andSTF-Kevlar are comparable, so that the STF-Kevlar is exhibiting superiorstab resistance relative to neat Kevlar on a per-weight basis.

TABLE 8 Stab performance of neat Kevlar and STF-impregnated Kevlartargets at different impact energies. All tests use a drop height of 10cm, and the NIJ “spike” end effector. Sample Number of Areal Drop ImpactImpact Witness Sample Density Mass Velocity Energy Papers TargetDescription (g/m²) (kg) (m/s) (J) Penetrated O 15 layers of 2670 2.331.35 2.13 3 neat Kevlar P 15 layers of 2670 2.74 1.29 2.28 4 neat KevlarQ 15 layers of 2670 3.14 1.35 2.88 4 neat Kevlar R 15 layers of 26703.60 1.35 3.30 5 neat Kevlar S 15 layers of 2670 4.01 1.35 3.66 5 neatKevlar T 15 layers of 2670 4.47 1.35 4.09 5 neat Kevlar U 12 layers of2650 2.33 1.44 2.42 0 STF-Kevlar V 12 layers of 2650 2.74 1.44 2.82 0STF-Kevlar W 12 layers of 2650 3.14 1.44 3.24 0 STF-Kevlar X 12 layersof 2650 3.60 1.44 3.74 0 STF-Kevlar Y 12 layers of 2650 4.01 1.44 4.14 0STF-Kevlar Z 12 layers of 2650 4.47 1.44 4.63 0 STF-Kevlar

The material can be used for advanced body armor, airbags, protectivematerial, such as for engines and turbines or anywhere that there is adesire to dissipate the kinetic energy of a moving object. The materialcan also be used for bomb blankets, tank skirts, stowable vehicle armor,inflatable protective devices, tents, seats or cockpits, storage andtransport of luggage, storage and transport of munitions, and sportinggoods or protective sports apparel. The material can be used to fashionprotective apparel or clothing, such as jackets, gloves, motorcycleprotective clothing, including jackets and hunting gaitors, chaps,pants, boots, which could stiffen to provide bodily protection againstblasts, such as those caused by exploding land mines, and suddenimpacts, such as those incurred upon landing by parachute, or inaccidents. The material would have stab resistance properties and can beused to provide bodily protection against sharp instruments, such asknives, picks, or swords used in hand-to-hand combat. The material alsocan be incorporated inside a helmet to protect the head, such asmotorcycle helmets, bicycle helmets, athletic helmets (football,lacrosse, ice-hockey etc). The material can also be used for industrialsafety clothing for protecting workers in environments where sharpobjects or projectiles could be encountered. The material can also beused for covering industrial equipment, such as equipment withhigh-speed rotating components, which could generate and releaseprojectiles upon catastrophic equipment failure. The material can alsobe used as shrouding over aircraft engines, to protect the aircraft andits occupants upon catastrophic failure of the engine. The material canalso be used as a spall liner for vehicles such as automobiles,aircraft, and boats, to protect the vehicle occupants by containingprojectiles generated by a blunt or ballistic impact on the outside ofthe vehicle. The material could also be used for puncture-resistantprotective clothing for fencing participants. The material could also beused in belts and hosing for industrial and automotive applications,

Fibre optic and electromechanical cables,

Friction linings (such as clutch plates and brake pads),

Gaskets for high temperature and pressure applications,

Adhesives and sealants,

Flame-resistant clothing,

composites,

asbestos replacement,

hot air filtration fabrics,

mechanical rubber goods reinforcement,

ropes and cables and

sail cloth.

All the references described above are incorporated by reference intheir entirety for all useful purposes.

As can be seen from the above description, the present inventionprovides an improved fabric for use in dissipating the kinetic energy ofa moving article. While the examples illustrate that the moving articleis a bullet or a spike, the moving article could also be flyingfragments, from an explosion, or a sharp instrument, such as a knife orsword thrusted into the wearer of the material or a stationary sharparticle just penetrating the material.

While specific preferred embodiments and materials have beenillustrated, described, and identified, it is to be understood that theinvention is in no way limited thereto, since modifications may be madeand other embodiments of the principles of this invention will occur tothose of skill in the art to which this invention pertains. Therefore,it is contemplated to cover any such modifications and other embodimentsas incorporate the features of this invention within the full lawfulscope of allowed claims as follows.

1. A material for dissipating the kinetic energy of a moving objectcomprising a fabric or a yarn which further comprises a shear thickeningfluid (STF) intercalated into said fabric and/or yarn wherein said STFremains in a fluid form and said STF comprises particles suspended in asolvent and said particle-solvent suspension remains in a flowable formafter intercalation and said solvent is environmentally stable andremains integral to said material and said suspended particles duringservice.
 2. The material as claimed in claim 1, wherein said material isa ballistic material which contains aramid fibers, graphite fibers,nylon fibers or glass fibers.
 3. The material as claimed in claim 1,wherein said particles are oxides, calcium carbonate, syntheticallyoccurring minerals, naturally occurring minerals, polymers or a mixturethereof.
 4. The material as claimed in claim 1, wherein said solvent iswater, which optionally contains added salts, surfactants, and/orpolymers and said material is a poly (para-phenylene terephthalamide).5. The material as claimed in claim 4, wherein said solvent is ethyleneglycol, polyethylene glycol, ethanol, silicon oils, phenyltrimethiconeor a mixture thereof and said material is a poly (para-phenyleneterephthalamide).
 6. A material for dissipating the kinetic energy of amoving object comprising a fabric or yarn which further comprises ashear thickening fluid (STF) intercalated into said fabric and/or yarnwherein said STF remains in a fluid form in said material duringservice.
 7. The material as claimed in claim 6, wherein said material isa ballistic material which contains aramid fibers, graphite fibers,nylon fibers or glass fibers.
 8. The material as claimed in claim 7,wherein said shear thickening fluid comprises particles suspended in asolvent.
 9. The material as claimed in claim 8, wherein said particlesare oxides, calcium carbonate, synthetically occurring minerals,naturally occurring minerals or polymers or a mixture thereof.
 10. Thematerial as claimed in claim 9, wherein said particles are SiO₂,polystyrene or polymethylmethacrylate.
 11. The material as claimed inclaim 10, wherein the solvent is water, which optionally contains addedsalts, surfactants, and/or polymers and said material is a poly(para-phenylene terephthalamide).
 12. The material as claimed in claim10, wherein said solvent is ethylene glycol, polyethylene glycol,ethanol, a silicon oil or phenyltrimethicone or mixtures thereof andsaid material is a poly (para-phenylene terephthalamide).
 13. Thematerial as claimed in claim 1, wherein said particles have an averagediameter size of less than 1 mm.
 14. The material as claimed in claim 1,wherein said particles have an average diameter size of less than 100microns.
 15. The material according to claim 6, wherein the materialcomprises one or more layers of said material and said at one or morelayers are a woven fabric.
 16. The material according to claim 6,wherein the material comprises one or more layers of said material andsaid at one or more layers are a nonwoven fabric.
 17. The materialaccording to claim 6, wherein the material comprises one or more layersof said material and said at one or more layers are a knitted fabric.18. The material according to claim 6, wherein at least a portion ofsaid polymer fibers are formed of poly (para-phenylene terephthalamide).19. A protective barrier comprising the material as claimed in claim 1.20. The protective barrier according to claim 19, wherein at least aportion of said polymer fibers are formed of poly (para-phenyleneterephthalamide).
 21. The protective barrier as claimed in claim 20,wherein the protective barrier is stowable vehicle armor, tents, seats,cockpits, spall liner, used in storage and transport of luggage, used instorage and transport of munitions.
 22. Body armor comprising thematerial as claimed in claim
 1. 23. An airbag comprising the material asclaimed in claim
 1. 24. A bomb blanket comprising the material asclaimed in claim
 1. 25. Protective clothing for protection fromfragmentation during activities as bomb defusing and demining comprisingthe material as claimed in claim
 1. 26. A tank skirt comprising thematerial as claimed in claim
 1. 27. A process for making the material,which comprises suspending particles in a solvent to form a shearthickening fluid and intercalating said shear thickening fluid inbetween yarns or fabrics of a material and wherein said STF remains in afluid form in said material during service.
 28. The process as claimedin claim 27, wherein said material is a ballistic material.
 29. A tirecomprising the material as claimed in claim
 1. 30. Industrial protectiveclothing comprising the material as claimed in claim
 1. 31. Industrialprotective materials and or liners for containing equipment or processesthat may produce fragmentation or projectiles, comprising the materialas claimed in claim
 1. 32. Protective clothing and equipment for sportsand leisure activities comprising the material as claimed in claim 1.33. The material as claimed in claim 1, wherein the material is used ina. belts and hosing for industrial and automotive applications, b. Fibreoptic and electromechanical cables, c. Friction linings (such as clutchplates and brake pads), d. Gaskets for high temperature and pressureapplications, e. Adhesives and sealants, f. Flame-resistant clothing, g.composites, h. asbestos replacement, i. hot air filtration fabrics, j.mechanical rubber goods reinforcement, k. ropes and cables l. insidehelmets m. fencing clothing n. motorcycle protective clothing o. boots,p. gaitors, q. chaps, r. pants s. gloves or t. sail cloth.
 34. Thematerial as claimed in claim 1, wherein the fabric or yarn is nylon. 35.A process of preventing an object to penetrate a person or structurewhich comprises covering said person or said structure with the materialas claimed in claim 1 so that at least part of said person or at leastpart of said structure is covered with said material and subjecting saidmaterial to an object to so that said person or said structure ismoving, said object is moving or both said object and said person orsaid structure is moving so tht the object partially penetrates saidmaterial.
 36. The material as claimed in claim 1, wherein said fabric oryarn is a polymeric fiber or yarn.